JOURNAL OF PROPULSION AND POWER Vol. 22, No. 6, November–December 2006 Overview of United States Space Propulsion Technology and Associated Space Transportation Systems Robert L. Sackheim∗ NASA Marshall Space Flight Center, Huntsville, Alabama 35812 DOI: 10.2514/1.23257 The space propulsion industry and, indeed, the overall space transportation industry in the United States have been in decline since the first human landing on the moon in 1969. The hoped-for reversal to this decline through the space shuttle and space station programs never really materialized. From an 80% market share in the late 1970s, the U.S. share of the world launch market fell to 20% by 2002. During that period, only two new booster engines have been developed and flight certified in this country. Only limited progress has been made in reducing engine costs or increasing performance although these factors are not necessarily directly related. Upper-stage and in-space propulsion in the United States have not fared much better in the world market. On the other hand, space-faring nations in Europe, the Middle East, Asia, and the former Soviet Union are believed to have developed 40–50 new, high-performance engines over the same period. This trend will have to be reversed to enable future exploration missions. The intent of this paper is to summarize past propulsion-system development, assess the current status of U.S. space propulsion, survey future options, evaluate potential impact of ultra low-cost, small launch-vehicle programs, and discuss some future propulsion needs for space exploration. I. Introduction In general, space transportation and rocket propulsion technology fl HE U.S. rocket propulsion industry and associated space development in the United States for all aspects of space ight applications has significantly lagged behind the rest of the world T transportation business has been in a steady state of decline fl fi since the end of the Apollo era (1972), although the actual steep since the initial ight certi cation of the space shuttle Space funding, and associated manpower, roll-off began immediately after Transportation System (STS). This lack of progress in advancing fi rocket propulsion technologies over such a long period has resulted the successful rst human landing on the moon, Apollo 11, in 1969. fi ’ A turnaround in the propulsion and space transportation industry was in several de ciencies in today s U.S. national space program. Most notable of these is the reduced reliability in U.S. launch and space expected after the space shuttle, and even, ultimately, the space fl station, program was authorized to proceed, but the turnaround never vehicles, as evidenced by the increased number of ight failures materialized. The space shuttle program [or National Space during the late 1990s and into the new decade, as well as the large loss Transportation System (NSTS)], which had to develop three new of U.S. market share in both the space launch and spacecraft industries. As is well known, the U.S. launch market share fell from liquid rocket engines [space shuttle main engine (SSME), orbital maneuvering engine (OME), and reaction control engine (RCE)] and 80% in the late 1970s to less than 20% worldwide in 2002. the world’s first large, segmented, and reusable solid rocket motor In the last three decades, only one new government-sponsored and one new largely commercial-sponsored booster engine have been did not reverse the decline from the Apollo era; it only slowed down fl fi the rate of decline until the late 1970s, as shown in Fig. 1. developed and gone through ight certi cation. These are the SSME and the Boeing RS-68, respectively. The SSME was, of course, Robert L. Sackheim just recently retired from NASA, after seven years as the Assistant Director and Chief Engineer for Propulsion at NASA’s George C. Marshall Space Flight Center (MSFC). He currently is an independent consultant and an adjunct professor at the University of Alabama, Huntsville (UAH). He holds a B.S. degree from the Downloaded by Univ of Wisconsin-Madison on October 8, 2012 | http://arc.aiaa.org DOI: 10.2514/1.23257 University of Virginia, an M.S. degree from Columbia University, and has completed all doctoral course work in chemical engineering at the University of California in Los Angeles. He joined MSFC after 35 years in various technical and management positions with the TRW Space and Electronics Group. His awards and honors include the AIAA James Wyld Award for outstanding technical contributions to the field of rocket propulsion, as well as 12 NASA Group Achievement Awards. While at TRW he received three annual Chairmen’s Awards and a TRW patent of the year award. He is a fellow of AIAA and was elected in 2000 to the National Academy of Engineering. He also received the AIAA Sustained Service Award in 2000. The Alabama/Mississippi section of the AIAA awarded him the Martin Schilling Award for outstanding service to the section, the Herman Oberth Award “For Outstanding Individual Scientific Achievement in the Fields of Astronautics and Space Sciences,” and the Helgar Toftoy Award for outstanding technical management. He recently received an award from the Association of Aeronautics and Astronautics of France for “High Quality Contributions to the Propulsion Field.” In 2001 he was awarded the NASA Medal for outstanding technical leadership, and in 2003 he was awarded a presidential citation for meritorious federal executive service. He has served on a number of NASA boards, including the Shuttle Independent Assessment Team (SIAT), the Mars Climate Orbiter Mishap Investigation Board, and the Mars Polar Lander Mishap Board. He has authored more than 250 technical papers. He also holds nine patents for spacecraft and/or launch vehicle propulsion and/or control systems technology. Received 21 February 2006; revision received 7 September 2006; accepted for publication 5 September 2006. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes. All other rights are reserved by the copyright owner. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code $10.00 in correspondence with the CCC. ∗Assistant Director and Chief Engineer for Propulsion (retired), Office of the Center Director. AIAA Fellow. 1310 SACKHEIM 1311 Apollo 11 missions. Many of these high-performance in-space propulsion First Lunar Era of the ICBMs plus Space technologies are literally required to enable many of the future space- Landing 100 Exploration and Science exploration missions planned for classes of human and robotic 90 spacecraft, as well as for many national defense missions. 80 Over 50,000 new high-tech jobs created Spawned the computer/information age 70 II. Importance and Key Functions of Space Propulsion 60 Pathfinder Space propulsion systems perform three basic but highly enabling 50 Initiation of SDIO X-vehicles the Shuttle functions for all U.S. payloads and assets that operate from space: 40 SLI, NGLT Program Orbital Space 1) They lift the launch vehicle and its payload from the Earth 30 Plane surface-based launch pad and place the payload into low Earth orbits 20 (LEO). 10 2) They transfer payloads from LEOs into higher orbits, such as % Peak Funding for Space Propulsion Space Propulsion PeakFunding for % geosynchronous, or into trajectories for planetary encounters 1960 1970 1980 1990 2000 (including planetary landers, rovers, and sample return launchers if Fig. 1 Historical trends in national rocket propulsion funding as a required). percentage of the peak funding for Apollo by year. 3) Finally, at the mission operational location, they provide thrust for orbit maintenance, rendezvous and docking, position control, station-keeping, and spacecraft attitude control (i.e., proper pointing originally developed for the space shuttle in the 1970s. Some and dynamic stability in inertial space). significant upgrades have been incorporated since the original Each of these sets of space propulsion functions provides unique, certification for flight, but their modifications have been to increase mission-enabling capabilities. The only type of rockets capable of reliability and safety and to somewhat improve reusable launch- providing high thrust forces required for an Earth-to-orbit (ETO) vehicle (RLV) operability [i.e., increase mean time between launcher are those that convert thermal energy to kinetic energy. refurbishment (MTBR) from one mission to another, on the order of Only two such technical approaches are conceivable today: 10–15 RLV flights]. Very little advancement in reducing costs or 1) chemical combustion and 2) nuclear reactor thermal power. increasing performance has been achieved. In fact, if anything, Nuclear thermal reactor rockets are unacceptable because they are performance and cost have been sacrificed to increase safety and open-cycle devices that emit radioactive materials. Thus, chemical reliability. rockets will launch NASA payloads into LEO for the foreseeable The RS-68 engine was developed by Boeing/Rocketdyne as a future. low-cost expendable booster engine for the Delta IV evolutionary It is also important to recognize that all flight experience with expendable launch vehicle (EELV). However, from published data chemical in-space propulsion systems [Apollo, satellites, planetary by the contractor, it did not meet its original target goals in spacecraft, shuttle reaction control system (RCS), and space station] nonrecurring and recurring (unit) costs and in performance. Engine has been with storable propellants. Other than the two- or three-burn performance of the RS-68 is comparable to that of the 1960s period Centaur/RL-10, the United States has never flown an in-space Saturn V second- and third-stage J-2 engines, both of which were propulsion system that uses cryogenic propellants, even though simple open-cycle, gas-generator powered designs.